The present invention relates to the handling of pipe sections of a drill string and, in particular to an apparatus for untightening the pipe sections.
A conventional drill rig typically includes a platform on which a mast is mounted. The mast carries a rotary head that is mounted for rotation and vertical movement relative to the mast. The rotary head is able to rotate and feed a drill string formed of pipe sections that are interconnected by screw threads. A pipe storage rack is sometimes mounted on or in the mast for receiving and dispensing pipe sections. The pipe sections are screwed together and fed into a bore hole. When it becomes necessary to pull drill string from the bore hole, the drill string is raised and the pipe sections are sequentially unscrewed from one another.
In a typical unscrewing operation, a first drill pipe section is rotated, while an adjacent second pipe section is held stationary. If the pipe sections are so tightly screwed together that they resist initial unscrewing efforts, special measures must be taken. For instance, one known untightening apparatus (e.g. see U.S. Pat. No. 4,194,419) includes an arm having multiple, relatively pivotable sections for rotating first pipe section, while a pair of jaws spaced vertically from the arm is provided for holding the second pipe section stationary.
The arm includes a main section mounted to a vertical post for rotation about a vertical axis of the post, an intermediate section mounted to the first section for rotation about a vertical axis defined by the drill pipe section, and a clamping section mounted on the second section for rotation about a vertical axis, whereby the first drill pipe section is gripped between the intermediate and clamping sections. A fluid cylinder interconnecting the main and intermediate sections rotates the intermediate section, the clamping section, and the first drill pipe section about the vertical axis of the first drill pipe section.
While this occurs, the two jaws, diametrically spaced from one another, are driven toward one another to engage non-cylindrical portions (e.g. flats) of an outer periphery of the second drill pipe section and thereby prevent the second drill pipe section from rotating.
The above-described arrangement has certain limitations, because the clamping section of the arm may not be ideally dimensioned for clamping pipe sections of different diameters. Also, the arm is of relatively complex structure due to the need to provide for relative pivotal movement between three arm sections.
Therefore, it would be desirable to provide an untightening mechanism and method which is of simplified, yet effective construction, and can be adapted to different diameters of pipe sections.